The present invention relates to an air intake control device that controls the throttle valve provided halfway through the air intake passage of an internal combustion engine (e.g. a gasoline engine and diesel engine), thereby adjusting the opening area of the air intake passage in response to the operating status of an engine. This air intake control device is used to control the intake air volume in the case of a gasoline engine, and is employed as a throttle mechanism of the air intake passage in the case of a diesel engine. The above air intake control device is described in Japanese laid-open Patent Publication Hei 03-271528.
The air intake control device for the diesel engine is designed to provide control in such a way as to secure a position slightly more open than the mechanically fully closed position to ensure that a sufficient space can be maintained between the valve and air intake wall surface even when the valve body is fully closed. This ensures that the engine does not stall even if the valve should fail to operate at the fully closed position for control purposes.
In order to ensure that the a predetermined volume of air flow leaks when the motor current is turned off, a throttle device for gasoline engine uses a so-called default mechanism according to the Japanese laid-open Patent Publication Hei 03-271528, for example, wherein the springs that produce a return force in the direction opposite to each other are provided between the valve operating gear and air intake device, and a lever, not stuck on the rotary shaft, is utilized between these two springs, whereby the throttle valve is forcibly opened by a predetermined angle when the motor current is off.